INTERNATIONAL JOURNAL OF ADVANCED RESEARCH IN … · radiological safety practices experienced in...

International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –

6480(Print), ISSN 0976 – 6499(Online), Volume 6, Issue 5, May (2015), pp. 75-91 © IAEME

75

RADIOLOGICAL SAFETY PRACTICES EXPERIENCED IN

HANDLING OF RADIOACTIVE SOURCE DURING

RADIOGRAPHIC TESTING, CALIBRATION AND RESPONSE

CHECK OF INSTRUMENTS DURING THE PROJECT STAGE OF

500 MWe PROTOTYPE FAST BREEDER REACTOR (PFBR)

Vidhya Sivasailanathan1, Prabhat Kumar

2, Dr.N.Manoharan

3, Dr.F.Emerson Solomon

4

1Health Physicist, Bharatiya NabhikiyaVidyut Nigam Limited, Department of Atomic

Energy,Kalpakkam – 603 102. Tamil Nadu. India & Research Scholar, AMET University,

Kanathur, Chennai

2Distinguished Scientist, DAE & Former Chairman & Managing Director, Bharatiya

NabhikiyaVidyut Nigam Limited,

Department of Atomic Energy, Kalpakkam – 603 102. Tamil Nadu. India & Research Supervisor,

Amet University, Kanathur, Chennai – 603 112. India

3Director Research, AMET University, Chennai, India.

4Associate Professor, Dept. of Bio-Medical Engineering, Bharath University, Chennai, India.

ABSTRACT

The presence and effect of ionizing radiation is detected and measured only with the help of

radiological instruments as radiation is non sensory. The radioactive half-life of the radionuclide

bears significance in assorting the radiation protection measures. The efficiency and resolution of

the radiation detection instrument is influential in detection of the contamination present on the

surface of the equipment and other materials lying on the floors and walls of the buildings emitting

alpha (α), beta (β), gamma (γ) radiations, neutron and gamma leaking out of reactor systems. Thus

they play a vital role in choosing the appropriate instruments to put into use for detection. The

efficiency of the instrument stands prompt to detect the presence of contamination and the resolution

helps identify the radionuclide which produces that contamination. The radiological instruments

which would consist of ion chamber, proportional counter, Geiger Muller tube, plastic scintillator

etc., need to be calibrated with a known radioactive source of appropriate strength of activity

depending upon the range of the instrument finalized. Preservation of radioactive source of any

strength of activity and handling of the same require the strict compliance to the radiation protection

INTERNATIONAL JOURNAL OF ADVANCED RESEARCH IN ENGINEERING

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ISSN 0976 - 6480 (Print) ISSN 0976 - 6499 (Online) Volume 6, Issue 5, May (2015), pp. 75-91 © IAEME: www.iaeme.com/ IJARET.asp

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76

procedures. In a nuclear power plant, where there is the routine use of radiological instruments,

larger equipment and radiological testing are a regular concern, the preservation of radioactive

sources and strict vigil of the handling the same is pivotal. The paper brings out the practical

experiences of handling of radioactive source of strength of various ranges for various activities

carried out at the project stage of Prototype Fast Breeder Reactor (PFBR).

Key words: Radiological Instruments, Non-Sensory, Efficiency, Resolution, Contamination And

Radioactive Source

INTRODUCTION

The Prototype Fast Breeder Reactor (PFBR) is a Uranium Oxide–Plutonium Oxide fuelled

fast neutron reactor, which employs liquid sodium as coolant, currently under construction at

Kalpakkam, near Chennai in India. Argon is used as the cover gas in the reactor. PFBR is the first of

its kind technology in power production in the nuclear industry in India and through which our

country is entering into the second stage of nuclear power programme.

There is a tremendous application of radiological source in nuclear power plants, medical,

agriculture, radiographic testing of the equipment, piping etc., considering the following scenarios.

As the nuclear industry involves the radioactive elements as fuel and the associated activation and

corrosion products emitting gamma rays, fission neutrons and photo neutrons as the sources of

radioactivity arising during operation of the reactor, it needs to be checked that all the instruments

are calibrated with a known strength of radioactive source. The areas where the radioactive sources

have been handled in PFBR during the pre-start up activities of commissioning of PFBR are:

� Radiographic Testing (RT): The option of handling of radioactive source involves testing of

components which are welded; to check the healthiness of the weld joints and compliance to

specifications as they are supposed to be leak tight.

� Response Check of in-core components: The application of radioactive source emerges

while irradiating the components which have to measure the neutron field inside and outside the

core. Such important components need to be calibrated and this also requires a response check with

a radioactive source (neutron or gamma).

� Response Check of Radiation Monitors: The area radiation monitors which are installed

inside the plant are also required to be calibrated with the appropriate strength of source before put

into operation.

� Response check and calibration of Health Physics Laboratory Instruments: The

radiological instruments in the Health Physics laboratory like survey meters, contamination

monitors, dosimeters, teletectors, neutron rem counters, etc., need to be calibrated with the

periodicity of time.

It becomes essential to identify the correct radioactive source, the required strength as per the

range of dose level to be fixed by the instrument. Further to these, the preservation of the radioactive

source, transportation of the radioactive source, careful handling of the source from not falling down,

missing etc., are to be strictly adhered to as per the stipulations and safety guidelines of the Atomic

Energy Regulatory Board (AERB).

The code of radiation protection is to minimize the exposure to personnel and environment

due to ionizing radiation. Thus handling of the source and adopting adequate radiation safety

measures in keeping the radiation exposure As Low As Reasonably Achievable (ALARA) to the

working personnel becomes the primary responsible of the Health Physicist of the plant. Keeping

the above points in view, the following activities are being carried out in Prototype Fast Breeder

Reactor.



77

INDUSTRIAL RADIOGRAPHY AT PFBR-RADIOGRAPHIC TESTING

The integration of the components at every stage involves welding. As the components in the

nuclear power plant are required to contain radioactivity and hazardous substance as no leakage is

permitted through the walls of the equipment or through any gaps that are left unwelded. The

flawlessness of the welding needs to be established before accepting any component. The weld

joints are checked for their healthiness by industrial radiography. In this process, ionizing radiation

is used to view the zones of the objects or joints in an equipment that cannot be seen otherwise. The

purpose of radiography does not alter the equipment dimension or does not make interaction with the

material of the equipment; but helps to view the presence of foreign materials inside an equipment

and ensure the perfection in the welding. Industrial radiography in other words is an element of non-

destructive testing. It is a method of inspecting instruments or materials for any hidden flaws by

using X-rays or gamma rays. These ionizing radiations would penetrate through the materials and

identify the flaws if any present. Gamma radiation sources of Iridium-192 and Cobalt -60 are

commonly used to inspect a variety of materials.

The healthiness of the pipelines can also be checked using Selenium-75 radioactive source of

strength of 80 Ci (Curie) and above. The techniques involved in the testing are single wall-single

image, double wall-double image and double wall-single image, The method and technique will be

suitably decided based on the dimension of the equipment and pipelines. The person who is carrying

out the test is accompanied by the Radiological Safety Officer, certified by The Bhabha Atomic

Research Centre, Mumbai.

In project phase, there will be a number of personnel working in the day time involving

various jobs. As a radiological safety measure, in order to avoid the exposure due to ionizing

radiation to a larger group of people, the testing at site will be carried out during night time when

there will be only limited number of personnel available in site. The testing area will be cordoned

off to keep the availability of the personnel from the centre of the radioactive source by keeping a

minimum distance. Since the testing process is continuous, the area gamma monitors are mounted in

the location to measure the background levels. The Thermo Luminescent Dosimeters have been

issued to the personnel involved in the testing.

RESPONSE CHECK OF IN-CORE COMPONENT: BORON COATED CHAMBER - IN

PFBR Boron Coated Chamber (BCC) is the in-core component used during initial fuel loading of

PFBR. The BCC is used for detection of neutrons during the first criticality of PFBR. Boron-10

Coated proportional Counters (BCC), with a sensitivity of 12cps/nv, are used in Control Plug during

initial fuel loading and first approach to criticality. To enhance the core monitoring, when the fission

chamber assembly attached to start up Neutron-Detector Handling Mechanism is lifted up and

moved away from the core region, in the control plug, during fuel loading. In case of long shut

down, if shut down count rate becomes <3cps, BCC with a sensitivity of 4cps/nv are used in control

plug to monitor the core during fuel loading and start-up. Before the counters are introduced in the

core, they need to be checked for response by neutron.



78

Fig 1: Control Plug

(Project inside reactor from top shield)

Fig 2: PFBR Reactor Assembly

1. Main Vessel

2. Core Support Structure

3. Core catcher

4. Grid Plate

5. Core

6. Inner Vessel



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7. Roof Slab

8. Large Rotatable Plug

9. Small Rotatable Plug

10. Control Plug

11. Absorber Rod Drive Mechanism

12. Transfer Arm

13. Intermediate Heat Exchanger (IHX)

14. Primary Sodium Pump (PSP)

15. Safety Vessel

16. Reactor Vault

SYSTEM DESCRIPTION

The Boron coated proportional counter has the detector diameter of 63mm and the detector

length is less than 1000mm. The neutron sensitivity is 12cps/nv.

SOURCE AND INSTRUMENTS

Americium-Beryllium source of strength 37 GBq (Giga Becquerel equivalent to 1 Curie) was

used to check the response of these detectors. The source provides neutron flux of 250 n/cm2/s when

placed with the detector on contact. The neutron rem counter is used to measure the neutron dose

rate and the associated cumulative dose if any. Gamma radiation survey was carried out in the

testing area using gamma survey meter before opening the source as well as after source was

removed from the shielding flask.

MEASUREMENTS

Following radiological levels were observed during the functional check of these detectors

using Neutron rem counter and gamma survey meters of two different make. The neutron field and

the gamma field at the distance of 1m from the source and on contact with source are measured.

Table 1: Gamma and neutron field at 1metre distance from the source and on contact

Source Distance

Field using Survey meter

Make 1 Make 2 Make 1 Make 2

@ 1m from

source

On

contact

@ 1m from source On contact

Neutro

n

0.015 mSv/h 1.5

mSv/h

- -

Gamm

a

- - 3 µSv/h 3.2 µSv/h 5.5mSV/

h

6mSV/

h

FUNCTIONAL CHECK OF BCC DETECTOR

The neutrons emitted from the radioactive source is fast neutrons. In order to slow down the

fast neutrons a thermalizing medium will be used. The High Density Poly Ethylene (HDPE) slabs

are sufficient enough to do this. During the functional check of the BCC detector, two HDPE slabs

each of thickness 3cm are used to thermalize the incident fast neutrons emitted from the Am-Be

source.

There are various positions of source and thermalizing medium with the detectors are

attempted and the output is observed in the electronics connected with the other end of the detector.

The signal output is also viewed in the Cathode Ray Oscilloscope (CRO) attached to the electronics.



80

The pictorial representation of the placing of the source and the thermalizing medium are shown as

below:

1. Background (absence of source)

The background counts are observed in the testing area using the gamma survey meters before the

source is brought to the field for testing.

2. Neutron Source –Thermalising medium – Detector (Contact neutron flux measurement)

2.1 Single Thermalising medium :

The source is placed in front of a Single HDPE slab and the emitted neutrons are allowed to

pass through the HDPE which is acting as a thermalizing medium for the fast neutron and reaches

the detector. The output signal is observed in the attached electronics.

Source (Am-Be) HDPE Detector

Fig 3: Single thermalizing medium set up

2.2 Double Thermalising medium:

The source is placed in front of double HDPE slab and the emitted neutrons are allowed to

pass through the HDPE which is acting as a thermalizing medium for the fast neutron and reaches

the detector. The output signal is observed in the attached electronics.

Source(Am-Be) HDPE Detector

Fig 4: Double thermalizing medium set up

3. Source – Detector – thermalising medium (Moderator outside)

The thermalising medium (HDPE) was placed after the detector. The fast neutrons are

directly hitting the detector and the escaped neutrons are backscattered by the thermalising medium

and once again reaches the detector.



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(Am-Be)Source Detector HDPE

Fig 5: Backscattering of the escaped neutrons hit the detector

4. On contact (For fast neutron measurement) :

The source is directly kept on the sensitive portion of the detector to observe the fast neutron

interaction.

(Am-Be)Source

Detector

Fig 6: Source is kept on contact with the detector

5. Collimated arrangement

5.1 For making the collimation arrangement of the source, the source is taken out and is directly

put inside the shielding flask in the vertical direction and placed towards the sensible portion of the

detector and the counts are observed for 10 seconds.

The observed count rate was 26.5 cps (counts per second) in the collimated arrangement.

Source in shield flask Detector

(Am-Be)

Fig 7: collimated set up of source to detector

5.2 With the same arrangement stated above, a collimating pipe is placed in front of the mouth of

the shielding flask of the source and thereby focusing the entire source to travel in one direction to

reach the sensible portion of the detector.



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The observed count rate was 29.5 cps in the collimated pipe arrangement.

Source in shield flask collimating beam Detector

Fig 8: collimated set up with a vertical pipe - source to detector

Calculation for the Minimum Detectable Activity of the Detector

Φ = __S___ n/cm2/s

4π R2

S is Source strength (1 Ci = 2.5X106 n/s).

R is Thickness of HDPE slabs used for thermalisation; in our case was approximately 3cm

Φ is the neutron flux

Substituting the values, we get,

2.5x106 = 2.5X10

4 cps (taking 108 as 100=10

2 for computation)

108

So, Φ = 2.5X104 n/cm

2/s

The value 2.5X104 cps corresponds to fast neutron flux. Due to thermalisation, 10% of the

flux value might be slowed down. Total thermal neutron flux reaching detector volume = 2.5X103

n/cm2/s.

Considering a 2π steradian, it is assumed that the 50% of the neutrons are reaching the

sensitive portion of the detector and it is expected that half the value of the flux will be observed as

counts. We shall have the 12cps sensitivity factor of the detector which corresponds to as 1 count.

So actual thermal neutron flux reaching detector =12500 n/cm2/s. Hence, minimum value in

the range of 12000 counts may be observed in electronics and the count rate is in the order of 1200

(as the counts are observed for 10 seconds). (The sensitivity factor = 12cps/nv for the detectors, 1

Count = 12cps).

The readings observed during the testing is tabulated as below:

Observation of count rate for background, with application of single thermalising medium,

double thermalising medium, on contact and outside the moderator with corresponding

response inference

Table 1: Observation of counts for various positions of source and thermalizing medium

Detector

No

Background

cps

Observed cps

Response Single

therm.

Double

therm. On contact

Outside

moderator

1 3.1 - 1255.3 58.0 1372.3 positive

2 2.1 - 1421.2 69.5 1306.3 positive

3 2.2 - 1260.2 35.4 1427.0 positive

4 1.6 - 1341.1 91.5 1340.0 positive

5 1.6 - 1228.8 70.2 1268.6 positive

6 1.8 - 1459.6 59.7 1287.3 positive

7 1.8 - 1331.7 52.3 1168.5 positive

8 1.5 - 1615.9 105.2 1385.3 positive



83

RADIOLOGICAL PROTECTION ASPECTS

The testing of a core component with a neutron source of 1Curie strength requires adequate

radiological protection measures to avoid the exposure to the personnel in the testing area.

TECHNOLOGICAL MEASURES

The position of the detector and the output part was designed to be in opposite ends. The

total length of the detector is 12metres. So the personnel working on the output end are available at

the distance of minimum 11.5 metres from the position of the source. The efficiency of the survey

meters are sufficient enough to observe the background counts and while the source is placed for

testing.

ADMINISTRATIVE CONTROLS

� The testing location was so chosen where there is no routine access of the building.

� During the testing period, access to the testing area was restricted to essential persons only.

� The source was brought to the field after duly ensuring that the electronics of the detectors are

responding well and calibrated.

� After every positioning of the source for a few seconds, the source was brought back inside the

shielding flask, during the interpretation of the observed output signals in the electronics.

� The source was handled by a tong of 1m long.

� As the detector assembly is 12m long, the electronics of the system is kept at the other end of

the sensible part of the detector.

� Despite all these only minimum people of the order of 15 were permitted to witness the

response check at the electronics end. No onlookers to view the performance of the testing is

strictly prohibited.

� The Health Physicists who were handling the source for the response check were issued with

Neutron badge, TLD and a DRD (Thermo luminescent and Direct Reading Dosimeters).

FINDINGS

The high temperature Boron Coated Chamber (BCC) responded to the neutron source at

varied settings of the instrument. Appreciable counts per second were recorded.

The dose exposure to the individual is NIL as per DRD issued to the personnel. The NIL

exposure indicates the discipline and the adequate adherence to the radiation protection measures

adopted and followed in our works and actions.

RESPONSE CHECK FOR RADIATION MONITORING SYSTEM AT PFBR

For the effective implementation of the design provisions for radiological protection for the

occupational workers, public and to the public, a well-defined radiation monitoring programme is

very much important. The radiation monitors which are designed under the Radiation Monitoring

System (RMS), monitor the radiation levels in all the potentially active areas and initiate

alarm/interlock actions as applicable. The RMS system is intended to measure, evaluate and record

all radiation exposures that are emerging in the operation and maintenance of the reactor. It is an

important activity of Health Physics Unit that all the radiation monitors are to be calibrated and

checked for response with the appropriate strength of radioactive source.



84

RESPONSE CHECK OF DETECTORS USED IN STACK MONITORING SYSTEM

The gaseous effluents releasing from Reactor Containment Building (RCB) is discharged

through 97.6m height stack which is closely located to Radioactive Waste Building (RWB). The

stack location is provided close to RWB in order to reduce the length of exhaust duct. The gaseous

effluents travel from low active zone to high active zone are collected at Reactor Containment

Building (RCB) and through Radioactive Waste Building (RWB), it passes through the filters in the

tunnel and discharged from the stack. The gaseous effluents of high value of radioactivity arises

from Active Argon and fission gases released from Primary Argon Cover Gas Circuit, Cover Gas

Purification System, Fission Gas Detection Circuit, Leak of cover gas containing fission product

gases, if any, into Reactor Containment Building and various cells etc.,

To measure the flow concentration at isokinetic point, the sampling air line drawn at the

height of 2/3 of total height of Ventilation stack is connected to the detectors in the stack monitoring

room. The sampling air will pass through the particulate activity detector (beta particles-Strontium-

90 is the representative radionuclide), Iodine activity detector (Iodine-131) and Stack Gamma

detector (Fission Product Noble Gases (FPNG) and Argon Activity detector). The FPNG and the

Argon activity indicates the gross gamma activity released during the operation of the reactor. The

sketch showing the schematic of arrangement of detectors in the stack monitoring room is noted in

Fig 9.

Fig 9: Schematic of Stack monitoring system

Stack Activity monitoring system consists of

i) Stack Particulate Monitor (Beta particles)

ii) Stack Iodine Monitor (Iodine -131)

iii) Stack Gamma Monitor (FPNG & Ar-41)



85

Table 2: Details of detectors used in the stack monitoring system

Fig 10: Stack Monitoring system Fig 11: Electronics in Stack monitoring system Fig 12: Ventilation stack

RADIATION PROTECTION MEASURES ADOPTED DURING THE TESTING

The radiation protection measures were carried out through technical and administrative

controls during the testing. They are discussed below:

S.No Detector Purpose of the

detector

Details of the detector Source used for response

1 Stack

particulate

activity

monitor

To monitor the

particulate

activities

released through

stack

Particulate filter, Plastic

Scintillation detector with

Photo Multiplier Tube

(PMT) along with Pre-

amplifier, Lead shielding

assembly and Electronic

Processing and Display

unit.

The radioactive source of

Strontium -90 of 1Bq was

used for the response check

of the detector. While

operating the ‘SYS RESET’

switch, the integral release

and output voltage were

verified.

2 Stack

Iodine

Monitor

To monitor the

Iodine-131

activities

released through

stack

Charcoal filter cartridge,

scintillation detector with

photomultiplier tube, Lead

shielding assembly and

Electronic Processing and

Display unit.


Barium-133 (disc source) of

1Bq was used for the

response check of the

detector. While operating

the ‘SYS RESET’ switch,

the integral release and

output voltage were

verified. The test is

repeated with Caesium-137

source.

3 Stack

Gamma

Monitor

To monitor the

gamma activities

released through

stack- to monitor

concentrations of

FPNG activities

and Argon-41

activity present

in the air stream

Gas chamber, Scintillation

detector with Photo

Multiplier Tube, Lead

shielding assembly and

Electronic Processing and

Display unit.


Caesium-137 (disc source)

of 1Bq was used for the

response check of the

detector.



86

TECHNICAL MEASURES

� The radioactivity of disc source as mentioned against each detector was used to check the

response of the detectors.

� By design of the plant layout, the stack monitoring room is situated in an isolated building

close to the Radioactive Waste Building (RWB).

� The testing was carried out inside the Stack Monitoring room itself, after enabling due power

supply to the detector and the electronic cabinet.


� The area was cordoned off with a sign of radioactive testing is going on though it is an

isolated location. Only essential personnel have been allowed to remain in the area to carry out the

response test.

� The background at the place was initially measured before the source was brought

� With the presence of source at each and every detector was checked for the response. The

response in the corresponding electronic cabinet is ensured for calibration.

FINDINGS

The exposure to the individual is NIL as per Direct Reading Dosimeter issued to testing

personnel.

RESPONSE CHECK OF PORTAL SURVEILLANCE MONITOR:

The Portal Surveillance monitoring system is required for monitoring the contamination on

personnel working in radioactive plant areas and to alert / alarm the personnel, on detection of

contamination.

The system consists of the Beta-Gamma Portal Monitor installed at the final exit point of the

plant and is used for monitoring the Head, Feet and other parts of the body of the personnel leaving

the areas prone to contamination. The system provides the local display of contamination data on all

the channels on a LCD screen and gives alarm and display when contamination exceeds the present

alarm level. In case of contamination, the system will also provide a contact output for external use.

All the detectors assemblies shall have pan cake GM tube detectors. Fig 13: Portal Monitor

sensitivity of the detector is high for Beta and low for gamma. The radioactive source used for the

response check is Strontium-90 with 3.7Bq (disc source). The detectors are placed for monitoring

head, body, hands and feet of the personnel. Suitable optical sensor has been provided to sense the

presence of the organs in the monitor. Suitable lead shields are provided to reduce the background

radiation level. The detector is made with sensitivity that it should respond for contamination or

clean within 3 seconds with 99% confidence level.



87

Fig 13: Portal Monitor

The radioactivity of Strontium-90 disc source with 3.7 Bq (Becquerel) was used to check the

response of the detector. The testing was carried out inside the Nuclear Island Connected Building

(NICB). The area was cordoned off with a sign of radioactive testing is going on. Only three

personnel were allowed to remain in the area to carry out the response test. The background at the

place was initially measured and with the presence of source at different chambers of the monitor

have been checked for the response. The audio annunciation in the system to inform

“Contamination” and “Clean” signals are verified.

RADIOLOGICAL PROTECTION MEASURES

The entire testing was carried out by following adequate radiological safety practices.

TECHNICAL MEASURES

� The radioactivity of disc source as required was used to check the response of the detectors.

� The location of the portal monitor is at the final exit point of the reactor. So the initial testing

were done on a holiday.

� The testing was carried out at the instrument location itself, after enabling due power supply

to the detector and the Electronic cabinet.


� The area was cordoned off with a sign of “radioactive testing is going on” though it is an

isolated location.

� Limited number of personnel were only permitted to remain in the area to carry out the

response test.

� The background at the place was initially measured before the source is brought

� With the presence of source the detector was checked for the response. The audio

annunciation in the system to inform “Contamination” and “Clean” signals are verified.

FINDINGS

The exposure to the individual is NIL as per Direct Reading Dosimeter issued to them.

The NIL value of the exposure represent the compliance to the highest standards of radiation

protection practices adopted while carrying out the testing in above cases and the success of

elaborate planning before any testing is initiated.



88

CALIBRATION AND RESPONSE CHECK OF HEALTHY PHYSICS LABORATORY

INSTRUMENTS

The prime responsibility of Health Physicist group in every nuclear power plant includes the

radiological surveillance. The Radiological surveillance in all zones is required to find the

background radiation level in the particular area. To meet this requirement different types of

radiation measuring instruments are procured, installed and calibrated. To measure the radiation

levels in zone 1 and office areas, Micro R Survey meter will be used and in other zone areas

teletector will be used for surveillance.

To identify the presence of contamination, Alscin (Alpha Scintillation Counter), survey meter

cum contamination monitors are used. To measure the air activity in controlled areas, air sampler is

used. The samples are analyzed using the filter paper in alpha counting and beta counting system

and the respective activity is estimated. The radioactive instruments are calibrated initially by the

supplier. However, the response check of the dosimeters will be done on procurement. The

instruments like survey meters, teletectors, counting systems, dosimeter like Thermo Luminescent

Dosimeter (TLD), Direct Reading Dosimeter (DRD) etc., need to be calibrated.

Fig 15: Alpha Counting System Fig 16: Teletector

CALIBRATION AND RESPONSE CHECK OF ANALOG DIRECT READING

DOSIMETER

The Direct Reading Dosimeters are issued to the occupational workers while carrying out

jobs in high potential areas along with Thermo Luminescent Dosimeter (TLD). The dosimeters need

to be calibrated and checked for response by exposing it to gamma radiation source. The dosimeter

has to be adjusted to zero in the aligning scale with fiber pointer. After doing zero adjustment, it

should be allowed for a minimum period of 24 hours to observe for any leak in the zero set point by

the fiber pointer. This is the leak test to be done for direct reading dosimeter.

Fig 17: DRD



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The initial reading after the leak test was noted and the dosimeter was exposed to the radioactive

source of Caesium-137 of 1 Ci (Curie) strength for 20 minutes to get the Fig 17: Analog DRD

exposure of 2mSv/h. This dose rate is achieved by keeping the dosimeter at a distance of 75cm from

the centre of the source.

Table 3: Response Check of DRDs

The readings are tabulated below:

RADIOLOGICAL SAFETY ASPECTS

The dosimeters are calibrated in the personnel calibration facility which is constructed as per

the safety requirement of regulators. The radioactive source will be operated pneumatically. By

setting the time of exposure in the control board and giving command for pneumatic operation of

opening of source, the personnel can move out of the facility. After completion of the set time, the

personnel can enter the facility and collect the dosimeters. Then the dosimeters reading can be seen

for functionality of the dosimeter. Since the personnel are absent when radioactive source is spared,

the exposure for the personnel is NIL.

The list of Health Physics lab instruments in PFBR and the periodicity of testing is as

follows:

Sl.No DRD No.

LEAK TEST RESPONSE CHECK

Initial

Reading

Final

Reading

Leak

for 24

hours

Initial

Reading

Final

Reading Net Error Error %

1 293746 0 0.0 0.0 0.1 1.9 1.8 0.2 10

2 293747 0 0.0 0.0 0.1 1.9 1.8 0.2 10

3 293748 0 0.0 0.0 0.1 2.0 1.9 0.1 5

4 293749 0 0.1 0.1 0.1 2.0 1.9 0.1 5

5 293750 0 0.0 0.0 0.0 1.8 1.8 0.2 10

6 293751 0 0.0 0.0 0.1 1.9 1.8 0.2 10

7 293752 0 0.0 0.0 0.1 2.0 1.9 0.1 5

8 293753 0 0.0 0.0 0.0 1.8 1.8 0.2 10

9 293754 0 0.0 0.0 0.1 1.9 1.8 0.2 10

10 293755 0 0.0 0.0 0.1 2.0 1.9 0.1 5



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Table 4: Frequency for Surveillance for the Health Physics lab Instruments used in PFBR

CONCLUSIONS

The use of radioactive source and handling of radiation arising from the source has been

optimized based on its requirement. The Radioactive source is to be stored, transported and handled

with necessary precautions as per the radiological safety guidelines of the regulators of our country

(AERB). The radiation protection procedure starts from the cordoning off the place and with

necessary sign boards where such radiological testing is to be carried out, the measurement of

background radiation level, the issue of dosimeters to log the individual exposure rate, safe handling

of the source while testing, lesser time taken to complete the response check, minimum of 1 metre

distance from the radioactive source during testing, etc., The above testings have been carried out

with due care taken for all such radiation protection measures and resulted with NIL exposure

experienced for the individuals. This successful completion of such testing with radiological source

testing with due precautions and adhering to the safe radiological practices have given confidence in

taking up further challenges in source handling by the crew or Prototype Fast Breeder Reactor

obviously.

S.

No Monitor

Source used

for calibration

Frequency of

Check Test Calibration

1 Survey meters (in use) Cs 137 Daily(II shift) ---- Once in 3 months(General

shift)

2 Survey meters (spares) Cs 137 Monthly (General

Shift) ----

Once in 6 months(General

shift)

3 Teletectors (in use) Cs 137 Daily(II shift) ---- Once in 6 months(General

shift)

4 Teletectors (spares) Cs 137 Monthly (General

Shift) ----

Once in 6 months(General

shift)

5 Rem counter Am-Be Daily(II shift) ---- Once in 6 months(General

shift)

6 α counting system in use Pu-239 Daily(each shift) ---- Once in a month (General

shift)

7 α counting system (spares) Pu-239 Monthly (General

Shift) ----

Once in 6 months (General

shift)

8 β counting system in use Sr90-Y 90 Daily (each shift) ---- Once in a month (General

shift)

9 β counting system (spares) Sr90-Y 90 Monthly (General

Shift) ----

Once in 6 months (General

shift)

10 Gamma counting system

(Single Channel Analyser)

Na-22 (disc

source)

11 Gamma counting systems

(Multi Channel Analyser)

Na-22 (disc

source) Daily(each shift)

Weekly

(III Shift)

Once in a month (General

shift)



91

ACKNOWLEDGEMENT

The author sincerely acknowledges the efforts and the guidance rendered by her supervisor

which has helped in dose reduction during construction stage and which has been reflected in the

form of dose reduction measures in this paper. The author also acknowledges the efforts of

personnel involved in all such radiological testing including BHAVINI and its contractors’

employees.

REFERENCES

1. The Evolution of ICRP recommendations 1977, 1990 and 2007

2. AERB Safety Guide on Security of Radioactive Sources in Radiation Facilities, AERB/RF-

RS/SG-1

3. AERB Safety Guide on Open Field Industrial Radiography, SG/IN-2

4. AERB Safety Guide on Radiation protection during operation of Nuclear Power Plants,

AERB/SG/O-5

5. The technical specification manual on in-core components of Prototype Fast Breeder Reactor

6. The installation document on Stack Monitoring System by Electronic Corporation of India

Limited

7. The installation document on Portal Surveillance Monitoring System by Electronic

Corporation of India Limited

8. Vidhya Sivasailanathan, et.al. “Radiological Safety Aspects in 500MWe Prototype Fast

Breeder Reactor (PFBR), Health Physics Professionals meet 2014 at AERB

9. Shivamurthy R.C, Manjunatha M B and Pradeep Kumar B.P, “Analysis of Contrast

Concentration For Radiological Images Using CBIR Framework” International journal of

Computer Engineering & Technology (IJCET), Volume 6, Issue 1, 2015, pp. 42 - 53, ISSN

Print: 0976 – 6367, ISSN Online: 0976 – 6375.

10. Apurva Patel and Vijay Savani, “A Design of Profibus Dp Slave Station Interface Card For

Modbus Based Intelligent Field Network Instruments” International journal of Electronics and

Communication Engineering &Technology (IJECET), Volume5, Issue 5, 2014, pp. 19 - 26,

ISSN Print: 0976- 6464, ISSN Online: 0976 –6472.

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